Just compared r128gain output versus ReplayGain for ref_pink.wav. ReplayGain defines ref_pink.wav as +6.00 dB. This was originally 0 when compared to 83 dB SPL but shifted up when 6 dB was added to make typical music "loud enough" on non-calibrated systems.

Since the whole point is to come up with a scaling ratio and relative LU are scaled in dB it looks to me like this algorithm will generate ReplayGain compatible values simply by adding 5.6 to the reported LU to compensate for the different base loudness of ref_pink.wav (-.4 difference due to fundamental differences in algorithms and +6 difference due to the ReplayGain reference point shift). However; this whole comparison is based on my assumption that the goal is to use the new algorithm for computing the loudness and adjustment but calibrating to the original reference sound. I don't know if this is a valid comparison or if for example the new algorithm would specifically not be expected to behave ideally on ref_pink.wav.

Anyway, for the few real music files I compared the results were similar enough to the ReplayGain calculated values that this seems plausible but different enough that I don't know if this is a valid conversion method or not.